Transmitter system comprising a plurality of interswitchable transmitters



y 6, 1968 TSUTOMU MIYAMOTQ 3,393,365

TRANSMITTER SYSTEM COMPRISING A PLUR'ALITY OF INTERSWITCHABLE TRANSMITTERS Filed Nov. 18, 1964 lnvenlor 7: MI M FO By l Allorney United States Patent 3,393,365 TRANSMITTER SYSTEM COMPRISING A PLURALITY 0F INTERSWITCHABLE TRANSMITTERS Tsutomu Miyamoto, Tokyo, Japan, assignor to Nippon Electric Company, Limited, Tokyo, Japan, a corporation of Japan Filed Nov. 18, 1964, Ser. No. 412,135 Claims priority, application Japan, Nov. 21, 1963, 38/ 62,637 6 Claims. (Cl. 325-129) ABSTRACT OF THE DISCLQSURE This application teaches a transmission system in which a plurality of transmitters all operable at the same frequency are coupled to a single output circuit. Each transmitter is comprised of an oscillator operating at a frequency f and a tuned circuit containing a variable reactive element which is tuned, under one condition, to a frequency nf where n is any real integer equal to or greater than 2. First bias means are provided for energizing only one of the group of transmitters and second bias means is provided for applying a bias to the variable reactive elements of all transmitters not coupled to the first bias means. The value of the bias means is selected so as to cause the outputs of all inoperative transmitters, when viewed from the output terminal, to appear as open circuits so as to cause substantially all of the energy generated by the operating transmitter to be passed to the output terminal. The variable reactive elements are preferably non-linear voltage controlled capacitor element of the diode type.

This invention relates to a transmitter system which is capable of supplying to an output terminal, such as the antenna, the output from any desired one of a plurality of transmitters, such as supplying the output of the working transmitter to the antenna, and wherein the antenna is also connected to one or more spare transmitters.

When a working and a spare transmitter are to be selectively connected to an antenna, it has been the practice heretofore to transmit the output of one of the transmitters to the antenna only. This required either a mechanical or electronic single-pole or double-pole doublethrow inter-switching switch for opening the connection between the antenna and one of the transmitters and closing the connection between the antenna and the other trasmitter. Alternately, short-circuiting pieces were disposed in the respective feeders which are provided by two branches of a T-shaped branch and the remaining branch was connected to the antenna. The first and second transmitters were positioned respectively in each of the two branches at points displaced by one-fourth wavelength of the transmitter output from the branching point of the T. The feeder leading to the spare transmitter with the associated short-circuiting piece is actually short circuited to provide a sufiiciently large impedance as seen from the branching point towards the spare transmitter. However, interposition of a mechanically movable part, such as the mechanical switch or the short-circuiting piece, in the feeder not only introduces the necessity for precise machining in order to maintain excellent impedance characteristics but also creates problems with regard to the electrical stability of the mechanical contacts. An electronic switch also introduces various problems. For example, if the transmitter output power is large, use must be made of large voltages or currents for controlling the diodes etc. contained in the electronic switch.

The object of the invention is therefore to provide a transmitter system including a plurality of transmitters 3,393,3fi5 Patented July 16, 1968 in which the transmitters can be rapidly interswitched without any mechanical switch while also requiring only a small control voltage or current.

According to the present invention, a plurality of transmitters are provided. Each transmitter has at the last stage thereof a frequency-multiplying portion including at least one non-linear reactance element (preferably a voltage controlled variable capacitance diode), only one of which produces the transmitter output. The transmitters are connected through the respective feeders to a branching point leading to the output terminal. In the transmitter producing an output the non-linear reactance element (variable capacitance diode) is greatly back biased while the transmitter is not in operation so that no frequency multiplication occurs and has the back biasing reduced when the transmitter is in service. According to this invention, the non-linear reactance element is supplied, while the transmitter (and hence the frequency multiplying portion including that reactance element) is not energized, with a direct-current bias from a separate direct-current biassing circuit. The bias can be preliminarily adjusted so that the impedance when viewed from the branching point to the non-excited transmitter will appear as an open circuit. Consequently, the transmitter output may be transmitted from the other energized transmitter to the output terminal only.

The above-mentioned and other features and objects of this invention and the means for attaining them will become more apparent and the invention itself will be best understood by reference to the following description of embodiments of the invention taken in conjunction with the accompanying drawings in which:

FIGS. 1 and 2 are circuit diagrams, partly shown in blocks, of two different embodiments of this invention.

Referring to FIG. 1, a first embodiment of the invention is illustrated therein. In FIG. 1, a first transmitter 13 includes as the last stage thereof a first frequencymultiplying stage 12. Stage 12 in turn includes a variable capacitance diode 11. A second transmitter 18 is also provided which in turn comprises at the last stage thereof a second frequency-multiplying stage 17. Stage 17 includes a second non-linear capacitive element 16. A T-shaped branch 20 is connected by feeders 21 and 22 respectively to the first and the second transmitters 13 and 18. The output terminal 23 of the T-shaped branch 20 may be connected to an antenna or other utilization device 8. A first and a second direct-current biassing circuit 26 and 27 are provided for supplying a direct-current bias to the non-linear capacitive element 11 or 16 contained in the non-energized transmitter. This bias is provided to make the impedance as viewed from branching points 251 and 252 of the T-shaped branch 20 towards the unenergized transmitter, to appear substantially as an open-circuit, as will be more fully described. A power source and control unit 30 is provided for selectively energizing (through leads 281 and 282) either the first or the second frequencymultiplying portions 12 and 17 and for controlling (through control leads 291 and 292) the direct-current biassing circuits 26 and 27. Control of the biassing circuits 26 and .27 is such that the biassing circuit for the unenergized frequency-multiplying portion will provide the above-mentioned direct-current bias.

The first transmitter 13 has an exciter portion 33 which includes an oscillator 31. This oscillator when energized by the power source and control unit 39 (through lead 281) produces an output oscillation having a frequency f. A tuning circuit 32 is provided which is tuned to the frequency f (approximately) and which is supplied with the output of the oscillator 31. The frequency-multiplying portion 12 of the first transmitter 13 includes the tuning circuit 36 which is composed of a capacitor 34, a coil 35 and diode 11 biassed by a suitable self-bias voltage. Tuning circuit 36 is tuned to a frequency it (where n is an integer at least equal to two) and is supplied with the output of exciter portion 33 through the non-linear capacitive element 11. An auto-biasing circuit including a bypass capacitor 37 and a resistor 38 is provided and adapted to supply, through the coil 35 and the coil 32 of the prior-stage tuning circuit, the non-linear capacitive element 11 with the bias voltage required for setting the non-linear element 11 into the desired frequency multiplying operation. An output coil 39 is inductively coupled to the coil 35 of the last-stage tuning circuit 36 and is adapted to deliver the transmitter output to the first feeder 21. The second transmitter 18 (and consequently the frequency-multiplying portion 17 thereof) is constructed in a manner similar to that for transmitter 13.

When the first transmitter 13 is energized, the exciter portion 33 thereof produces output oscillations having the frequency f. Exciter portion 33 is supplied with power from power source and control unit 30 over lead 231. Harmonics of the frequency f are generated by the nonlinear element 11 (supplied with the bias voltage from the auto-biassing circuit). The frequency-multiplied oscillation having a frequency 22 (contained in the harmonics as the main component) is then extracted by the laststage tuning circuit 36. The transmitter output having a frequency nf is then picked up by the output coil 39 (coupled to the last-stage tuning circuit 36) and is delivered through the first feeder 21 to the T-shaped branch 20.

The second transmitter 18 operates in a manner similar to that of transmitter 13. Thus transmitter 13 is driven by power source and control unit 39 through lead 282. The power source and control unit 30 operates however to de-energize the first transmitter 13 through the lead 281. When the first transmitter 13 is thus out of operation, the tuning circuit 32 in the exciter portion 33 of this transmitter 13 serves as a substantial short circuit for the electrical oscillation of the frequency it because the capacitor of tuning circuit 32 has a capacity which tunes circuit 32 to the frequency Furthermore, as is evident, the by-pass capacitor 37 in the first frequency-multiplying portion 12 is also short-circuited for the oscillation of the frequency n1. Meanwhile, the second direct-current biassing circuit 27 is controlled through lead 232 by the power source and control unit 30 to stop the supply of any additional direct-current bias to the second non-linear capacitive element 16 so as to cause the second frequencymultiplying portion 17 to produce the preset frequency and thus make the second transmitter 18 produce the output frequency 21 Thus, it is seen that the first directcurrent biassing circuit 26 is controlled by the power source and control unit 30 to apply the aforementioned direct-current bias to the first non-linear capacitive element 11 to control the capacitance thereof. Consequently, if the loss in the first non-linear capacitive element 11 and the tuning circuits 32 and 36 are neglected (for the sake of simplicity) the impedance when viewed from the first feeder 21 towards the first frequency-multiplying portion 12 will have no resistive component, and will merely have a reactive component X (j is the imaginary unit). Therefore, this impedance can be placed in the open-circuited condition for oscillations having the frequency n This condition is seen when looking toward the first frequencyrnultiplying portion 12 along feeder 21 from a certain point or from points displaced from that certain point by integral multiples of the half wavelength of the electromagnetic wave of the frequency nf. The positions of these points depends upon the reactive component 'X which in turn depends on the capacity of the first voltage controlled variable capacitive elernent 11 which is controlled by the direct-current bias voltage supplied from the first direct-current biassing circuit 26. It can, however, be very troublesome to calculate the positions of such points for a given reactive component jX. To determine the positions of these points by experiment also will require complicated measurements. It is therefore contemplated according to this invention to utilize the fact that the positions of such points are adjustable within a limited region. This adjusting can be achieved by varying the value of the bias supplied to capacitive element 11 from the biassing circuit 26. Thus, the direct-current bias supplied to the first non-linear capacitive element 11 from biassing circuit 26 should be preset to a value such that the impedance viewed from the branching points 251 and 252 of the T-shaped branch 20 will be substantially in the open-circuited state.

As mentioned in the preceding paragraph, it is possible with the transmitter system of this invention to transmit, (when the first transmitter 13 is out of service and the second transmitter 18 is in operation) the energy produced only by transmitter 18 to the output terminal 23 by merely causing that impedance to be substantially in the open-circuited state for the transmitter output of the frequency nf of either transmitter 13 or 18. This open circuit condition is to exist when viewing transmitter 13 from the branching points 251 and 252 of the T- shaped branch 20. When the operation of the second transmitter 1 8 is discontinued by de-energization thereof, the control action provided through the first control lead 291 to the first direct-current biassing circuit 26 discontinues application of the direct-current bias to the first non-linear capacitive element 11. At the same time, the energy supplied through lead 281 to the first transmitter 13 causes transmitter 13 to transmit the output frequency nf thereof to the T-shaped branch 20. Furthermore, the control signals furnished through lead 292 to the biassing circuit 27 causes a bias to be applied to non-linear capacitive element 16. This direct-current bias, replaces the auto-bias supplied by the auto-biassing circuit connected to the non-linear capacitive element 16. The thus supplied DC. bias will make the impedance seen from the T- shaped branch 20 towards the second transmitter 18 appear as an open-circuit for the transmitter output frequency n7 supplied by the first transmitter 13. In this case, the output of the first transmitter 13 is supplied only to the output terminal 23. In this manner, it is possible with a transmitter system of the invention to transmit the output of the working transmitter to the antenna alone, without any transmission to the spare transmitter which produces no output. Incidentally, it will be understood that the power source and control unit 30 may merely be a power source and a conventional switch, such as an electronic switch.

If transmitters 13 and 18 are transistorized transmitters (as is often the case) either will be able to produce a transmitter output as soon as it is energized by the power source and control unit 30. It is therefore possible to state (even though the spare transmitter is not preliminarily in operation) that the time required for switching from the working transmitter to the spare one is equal to the switch-over time of the electronic or other switch used in the power source and control unit 30.

Referring to FIG. 2, there is illustrated therein another embodiment of this invention. In FIG. 2, reference numerals corresponding to those in FIG. 1 will indicate similiar operation or components. FIG. 2 illustrates a UHF transmitter system. The first transmitter 13 includes at the last stage thereof a first frequency-multiplying portion 12 which in turn includes, the non-linear capacitive elements 11 and 11'. The second transmitter 18 includes at the last stage thereof a second frequency-multiplying portion 17 which in turn includes a second set of nonlinear capacitive elements 16 and 16'. First and second feeders 21 and 22 connect the T-shaped branch 20 to the first and the second transmitters 13 and 18, respectively. The output terminal 23 of the T-shaped branch 20 is connected to an antenna or other utilization device (not shown). First and second direct-current biassing circuits 25 and 27 are provided respectively for the first and second transmitters 13 and 18 and are adapted to supply the set of non-linear capacitive elements (11 and 11' or 16 and 16) of the unenergized transmitters with a direct current bias which will cause the impedance when viewed from a branching point 25 towards that frequencymultiplying portion 12 or 17 to appear as an open-circuit. A power source and control unit 30 is provided for energizing (through leads 281 and 282) either one of the frequency-multiplying portions 12 and 17 and for controlling (through control leads 291 and 292) either one of the direct-current biassing circuits 26 and 27. The control is such that the biassing circuits (26 or 27) for the non-energized frequency-multiplying portion will supply the above-mentioned direct-current bias.

The first transmitter 13 includes an exciter portion 33 which includes: an oscillator 31 for producing oscillations having a frequency f. Oscillator 31 is energized by the power source and control unit 30 through lead 281. An output coil is provided for coupling the output of the oscillator 31 to the next succeeding stage. A tuning coil is divided by a neutral tap into two tuning coil portions 35 and 35' which form series resonance circuits respectively, with the capacities of the respective associated non-linear capacitive elements 11 and 11' (which capacities appear when the frequency-multiplying portion 12 is in operation). Coils 35 and 35' are inductively coupled to the oscillator output coil 310. Each non-linear capacitive element 11 and 11' is respectively connected in parallel with a resistor 38 or 38' which constitutes an autobiassing circuit for supplying the non-linear capacitive element 11 or 11' with a bias which will permit the nonlinear capacitive element 11 or 11' to perform the desired frequency-multiplying function and forms together with the tuning coil portion 35 or 35' a series resonance circuit (corresponding to 32 of FIG. 1) for the frequency f when the oscillator 31 is in operation. Diodes 41 and 41' maintain (while oscillator 31 is in service) the autobias supplied to the non-linear capacitive elements 11 and 11' from the respective auto-biassing circuits. Diodes 41 and 41 supply (While the oscillator 31 is not in operation) the direct-current bias from the direct-current biassing circuit 26 to the respective non-linear capacitive elements 11 and 11'. Coils 42 and 42' are provided to isolate (with respect to high frequency) the respective circuit portions including the respective non-linear capacitive elements 11 and 11' from the diodes 41 and 41, and consequently both of said circuit portions from the directcurrent biassing circuit 26. The frequency-multiplying portion 12 of the first transmitter 13 includes some of the components of the exciter portion 33. In fact, it includes all the elements of exciter 33 except for oscillator 31 and the oscillator output coil 310.

A series coil 45 and a series variable capacitor 46 are connected in series between the neutral tap dividing the tuning coil portions 35 and 35' and the inner conductor of a coaxial cable which serves in the illustrated embodiment as the first feeder 21. A parallel coil 47 and a parallel variable capacitor 48 connect the inner and the outer conductors of the first feeder 21. Coils 45 and 47 and capacitors 46 and 48 taken together form with the abovementioned common portion (particularly with the non linear capacitive elements 11 and 11' and the tuning coil portions 35 and 35') a last-stage tuning circuit which is tuned to the frequency nf (where n is an integer at least equal to two) and also forms a matching circuit between the frequency-multiplying portion 12 itself and the first feeder 21. The first direct-current biassing circuit 26 connected to the first transmitter 13 includes: a terminal 51 which is supplied by lead 291 with a negative direct-current voltage from the power source and control unit 30 only when power is supplied from unit 30 to lead 282. Thus, circuit 26 will be controlled by signals on lead 291 to supply both non-linear capacitive elements 11 and 11' with a direct-current bias which will replace the respective auto-bias voltages. A potentiometer-resistor 52 is connected between terminal 51 and ground and is provided with a sliding contact 52a. The second transmitter 18 and consequently its frequencymultiplying portion 17 and the accompanying directcurrent biassing circuit 27 all have the same construction indicated for corresponding portions of transmitter 13.

If the transmitter 13 is energized by energy supplied over lead 281 from unit 30, it will deliver an output having the frequency nf as was the case with the embodiment of FIG. 1. In this case, the second transmitter 18 is not energized by energy supplied on lead 282. Moreover, no control signals are supplied to the direct current biassing circuit 26 over lead 291. Thus, the first set of voltage controlled variable capacitance elements 11 and 11 are not supplied with any additional directcurrent bias from the first direct-current biassing circuit 26 but rather are supplied with the auto-bias from the respective auto-biassing circuits. If the second transmitter 1 8 is energized by energy supplied over lead 282 from the unit 30, the transmitter 18 will deliver its output having the frequency n to the second feeder 22. In this latter case, the control signals appearing on lead 291 will cause the direct-current biassing circuit 26 to supply the non-linear capacitive elements 11 and 11' with a pre-adjusted direct-current bias (which is adjusted by the potentiometer-resistor 52) in place of the autobias. Since the resistance of the parallel resistors 38 and 38' (for supplying the respective auto-bias voltage) respectively can be as high as several hundred kiloohms, it follows that if the loss in the non-linear capacitive elements 11 and 11', the tuning coil portions 35 and 35', the series and the parallel coils 45 and 27, the series and the parallel capacitors 46 and 48 etc. are neglected (for the sake of simplicity) the impedance when viewed from the first feeder 21 towards the first transmitter 13 will have no resistive component and in fact will be a pure reactive component 'X (j is the imaginary unit). This is similar to the operation of the embodiment of FIG. 1. Thus, it is possible to make the impedance when viewed from the branching point 25 towards the first transmitter 13 appear as an open-circuit for the oscillations having the frequency nf. This can be done by empirically pre-setting the branching point 25 along the first feeder 21 at a generally favorable position and preadjustin-g (by means of the potentiometer-resistor 52) the direct-current bias to be supplied to the non-linear capacitive elements 11 and 11' from the first direct-current biassing circuit 26. Thus, the embodiment of FIG. 2 operates in a manner similar to the embodiment of FIG. 1.

Measurements were actually obtained from a transmitter system which was assembled in accordance with FIG. 2. The transmitter provided output power of about 6 W. with the frequency set at 400 mc. For this transmitter it was not possible to make the impedance (when viewed from the branching point of the T-shaped branch towards that transmitter which was delivering no output) appear as a perfect open-circuit because of the loss in the non-linear capacitive elements, the tuning coils, etc. However, it was possible to keep the loss of the transmitter output delivered to the output terminal of the T-shaped branch from the transmitters which is producing the output, within 0.5 db.

While the invention heretofore explained had a first and a second transmitter connected to a branching point through a first and a second feeder, respectively, the invention is equally well adaptable to a transmitter system having more than two transmitters connected to a branching point through a corresponding number of feeders, respectively. Incidentally, the word bias as used herein should be understood to mean a bias voltage if the nonlinear reactance element is a non-linear capacitive ele ment (such as used in the embodiment) and a bias current if the non-linear reactive element is any one of the known non-linear inductive elements. Additionally, it will be obvious that the DC. bias supplied by unit 30 through bias sources 26 and 27 could be altered such that the biassing energy is derived from the working transmitter and 'which is then fed to each of the spare transmitters. Thus, as long as the working transmitter was operative, the spare transmitters would be isolated therefrom.

While I have described above the principles of my invention in connection with specific embodiments, it is to be clearly understood that this description is made only by way of example, and not as a limitation to the scope of my invention as set forth in the objects thereof and in the accompanying claims.

What is claimed is:

1. In a transmitter system having a plurality of transmitters connected to the same common output terminal for operation of only one of said transmitters at any given time while the remaining transmitters are retained in standby condition, improved isolating means for isolating all but one of said transmitters from said output terminal comprising: a tuned circuit including a voltage controlled variable reactance element in the output stage of each transmitter; a plurality of feeder circuits each being of a predetermined length coupled between an associated tuned circuit and said common output terminal; and means selectively connected to all but one of said tuned circuits at any given instant for controlling the variable reactive elements of all but one of said transmitters, such that the impedance of each transmitter maintained in standby considered in conjunction with its feeder circuit, when viewed from the output terminal, will appear to be substantially an open circuit.

2. In a transmitter system as set forth in claim 1 wherein the control means further includes a separate DC. biasing circuit connected to each non-linear reactance device in each transmitter, said separate DC. biasing circuits for each transmitter supplying the controlled DC. bias to the non-linear reactance element connected thereto only when its associated transmitter is selected to be deenergized.

3. A transmitter system comprising: a plurality of transmitters, each transmitter including a tuned stage having a voltage controlled variable reactance means therein; an output terminal; feeder circuits for connecting the tuned output stage of each of said transmitters to said output terminal; means selectively connected to the nonlinear reactance means in selected ones of said transmitters for supplying a controlled DC. bias signal only to the re-actances in the transmitters to be maintained in standby condition, said bias signal controlling the impedance of each non-linear reactive means such that the impedance of each standby transmitter tuned output stage and feeder circuit, when viewed from the output terminal appears to be substantially an open circuit whereby the working transmitter will be effectively isolated from the standby transmitters enabling substantially all of the output signals from the working transmitter to be fed to the output terminal.

4. A transmitter system comprised of a plurality of transmitters each having a tuned circuit including :1 voltage controlled variable reactance element;

an output terminal;

a plurality of feeder circuits of predetermined length each coupling an associated tuned circuit of each transmitter in common to said output terminal;

first bias means for selectively energizing only one of said transmitters at any given instant;

a plurality of self biasing circuits each coupled to an associated reactive element for tuning the associated tuned circuit to be resonant at a frequency nf where n is a real integer greater than 1;

second bias means for applying a large back bias to the reactive elements greater in value than said self biasing circuits being selectively coupled to the reactive elements of all but the energized transmitter, causing those tuned circuits so energized, when viewed from the output terminal and through their associated feeder circuit, to appear as an open circuit.

5. A transmitter system including at least two transmitters, each having a final output stage;

each of said final output stages being comprised of a frequency multiplying portion including at least one voltage controlled variable capacitance diode and a tuning circuit including said diode for extracting a frequency multiplied output of its transmitter signal which is n times the operating frequency of the transmitter signal where n is a real integer;

a biasing circuit for selectively applying a control voltage to said variable capacitance diode for back biasing the diode for preventing the diode from performing the desired frequency-multiplying operation and thereby changing the reactance of the tuning circuit to a finite apparent reactance by the detuning operation;

an output terminal for said system and a junction terminal coupled to said output terminal;

a plurality of feeders each connecting the final output stage of an associated transmitter to said junction point;

means for selectively controlling the biasing circuits of each transmitter to place only one of said transmitters in the operating state while the remaining transmitters are placed in standby state;

the length of each of said feeders from said junction point to the output of its associated final output stage being selected so that the impedance at the junction point looking toward said finite reactance of the final output stage of a transmitter in standby state is infinite at said desired frequency.

6. The transmitter system of claim 5 wherein said control voltage means is further comprised of means for selectively energizing only one of said transmitters at any given instant while the remaining transmitters are in a deenergized state during standby.

References Cited UNITED STATES PATENTS 2,855,525 10/1958 Schunemann 325129 X 3,056,127 9/1962 Harris 3435 2,270,771 1/1942 Schonfeld 331-49 2,385,673 9/1945 Woodworth 32551 X 2,692,338 10/1954 Moore 328-154 X 2,753,454 7/1956 Parker 325-129 X 3,158,692 11/1964 Gerkensmeirer 17915 FOREIGN PATENTS 587,063 11/ 1959 Canada.

ROBERT L. GRIFFIN, Primary Examiner.

DAVID G. REDINBAUGH, JOHN W. CALDWELL,

Examiners. B. V. SAFOUREK, Assistant Examiner. 

